Earthquakes and any otherwise generated ground movements can have devastating effects on structures and machinery. Since large parts of the world are susceptible to earthquakes it is unavoidable that industrial structures will occasionally be subjected to earthquakes. Certain industrial structures must therefore be effectively protected from the effects of earthquakes to avoid subsequent disasters that can be as dangerous as the original shock. Examples of facilities that must be so protected include nuclear power plants, chemical refining plants and military facilities housing armaments. At such facilities leaks of radioactive or poisonous chemicals and the possibility of explosions must be avoided.
Large shock absorbing devices have been devised which minimize the acceleration of the mass of a mechanism or housing with respect to its support or foundation. Simple shock mounts include elastic pads or insulation, massive springs and hydraulic pistons. None of these types of devices are completely satisfactory.
Elastic pads and damped springs absorb shock through movement and heating of their elastic material. Unfortunately, elastic pads and springs often overreact to step inputs and as a result can, depending on the frequency of the shocks, worsen the effect of the shocks through resonant oscillations. In many applications these resonant frequencies can be avoided, but not, however, for ground shocks which are largely unpredictable in frequency and intensity.
Hydraulic piston shock absorbers, also called dashpot or liquid springs, absorb the energy of the mass in motion by forcing fluid through restrictions as a piston is driven through fluid by the shock. Heat generated thereby is dissipated by radiation and conduction from the shock absorber. There are several difficulties with this type of device when used to absorb massive shocks. Massive shock absorber pistons respond to shocks very slowly which means that rapid shock impulses are transmitted through the shock absorber to the protected device. Hydraulic fluid pressure adjacent to the piston can also rise too rapidly as a result of piston movement. Excessively high hydraulic pressure can cause shock absorber failure through leakage and fracture. As a result, larger hydraulic pistons are equipped with pressure relief valves that bypass fluid around the piston when fluid pressure exceeds a certain level.
Relief valves must exhibit high response rates and high flow rates to be effective. The relief valves are therefore subject to problems similar to those of the shock absorber. If the pressure relief valve is tied to the piston or a stiff spring it will respond too slowly to rapid shock driven pressure rises; if the pressure relief valve is triggered by dynamic masses and springs it may overreact to step input demand and oscillate.
The unfortunate choice for both shock absorber pistons and pressure relief valves is between heavily damped devices which are slow to respond, or lightly damped devices which tend to overreact and oscillate.
This invention's objective is to overcome the above problems with a device that uses a combination of hydraulics and springs that operate differently in response to different inputs of varying intensity and duration. The objectives of this invention also include producing a device with the ability to absorb shocks and dampen the transmission of vibration over very large spectrum of possible shock inputs.